1. Field of the invention
The present invention relates to a method and an apparatus for positioning the head of a patient accurately for tomographic x-ray imaging of a selected cross-sectional plane through the mandible or maxilla of the patient.
The method and the apparatus of the present invention are designed particularly, although by no means exclusively, for use with existing tomographic apparatus installed, for example, in dental professional offices and used for site evaluation of the mandible and the maxilla prior to installing osseointegrated implant posts to support various dental prosthesis. More particularly, the present invention is concerned with a method and an apparatus for precisely locating the patient in relation to a tomographic apparatus such that the site of the anatomy of interest is at the correct position to provide an accurate tomographic x-ray of the site.
2. Description of the Prior Art
By way of background, the dental profession has been involved to an increasing degree with the osseointegrated implant system to facilitate dental prosthesis.
In order to properly install an implant a tomographic x-ray of the proposed site should be taken so that the dentist can investigate the adequacy of the osseous tissue to support an implant post at that site. The x-ray of the mandible or maxilla should employ tomography in order to project the cross-sectional area of the mandible or maxilla at the site.
X-ray tomography involves rotating an x-ray source and a photographic plate in an arc relative to a patient during exposure of the x-ray image. Specifically, the x-ray source and the photographic plate are rotated through an arc about a central axis that is perpendicular to the x-ray beam. The result of such movement is that all bone structure in front and behind a vertical plane through the central axis are blurred and essentially do not appear in the image. The vertical plane through the central axis is hereinafter referred to as the "tomographic plane".
Thus, only that structure located at the tomographic plane appears in the x-ray image so that the image is of a cross-section of the bone tissue. Therefore, by positioning the head of a patient so that a cross-sectional area which includes a particular site of interest of the mandible or maxilla of a patient coincides with the tomographic plane it is possible to obtain an x-ray image of the particular site of interest.
Clearly, an important consideration in the use of x-ray tomography is the accurate positioning of the anatomy of interest in the tomographic plane.
U.S. Pat. No. 4,974,243 entitled "Positioning System for a X-Ray Tomography" assigned to AxialTome Corporation discloses a method and an apparatus for such accurate positioning of the head of a patient in relation to a tomographic apparatus which works effectively in many situations.